AT&T 7100 series User Manual
MULTIPLEXED COMMUNICATION
1-27
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Facilities using RBS carry digital data at 56 kbps. They can be used to carry voice, voice-grade data, or
data that uses only 56 kbps of the available 64-kbps bandwidth (for example, mode-1 data).
data that uses only 56 kbps of the available 64-kbps bandwidth (for example, mode-1 data).
24th-Channel Signaling
24th-channel signaling permits the channels to use their full 64 kbps bandwidth capacity. This type of
signaling provides 23 64-kbps channels for voice or data transmission, with the 24th channel reserved for
signaling only.
signaling provides 23 64-kbps channels for voice or data transmission, with the 24th channel reserved for
signaling only.
The format used to carry signaling information requires a 24-frame superframe. ESF meets this
requirement. For D4 framing to meet this requirement, however, two D4 frames are linked together to form
the required 24-frame superframe.
requirement. For D4 framing to meet this requirement, however, two D4 frames are linked together to form
the required 24-frame superframe.
There are three variations of 24th-channel signaling:
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AT&T proprietary signaling
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DMI BOS (bit-oriented signaling)
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ISDN-PRI (sometimes called DMI MOS, or DMI message-oriented signaling)
Table 1-8, 24th-Channel Signaling Arrangement, depicts the frame number and signaling channel
relationship used for DMI BOS (many other relationship rotations are possible).
relationship used for DMI BOS (many other relationship rotations are possible).
Table 1-8. 24th-Channel Signaling Arrangement — DMI BOS
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Channels
24th Channel
24th Channel
Channels
24th Channel
24th Channel
1-23
D4 ESF
1-23
D4 ESF
Frame No.
Frame No.
Frame No.
Frame No.
Frame No.
Frame No.
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1 1 13
13 1 1
2 2 14
14 2 2
3 3 15
15 3 3
4 4 16
16 4 4
5 5 17
17 5 5
6 6 18
18 6 6
7 7 19
19 7 7
8 8 20
20 8 8
9 9 21
21 9 9
10 10 22 22 10 10
11 11 23 23 11 11
12 12 24 24 12 12
11 11 23 23 11 11
12 12 24 24 12 12
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AT&T proprietary signaling was the first type of 24th-channel signaling provided by System 75 and
System 85. It was developed to carry DCP-formatted data (in digital form) between System 75 and/or
System 85 switches. AT&T proprietary signaling is described in the initial release of the DMI technical
specification.
System 85. It was developed to carry DCP-formatted data (in digital form) between System 75 and/or
System 85 switches. AT&T proprietary signaling is described in the initial release of the DMI technical
specification.
For AT&T proprietary signaling, a complete set of signaling information is sent every 24 frames. This 24-
frame period is not synchronized to the 12-frame superframe format of D4 framing or to the 24-frame
superframe format of ESF framing. Each signaling byte contains the equivalent of a channel identification
frame period is not synchronized to the 12-frame superframe format of D4 framing or to the 24-frame
superframe format of ESF framing. Each signaling byte contains the equivalent of a channel identification